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CN116907177A - Nitrogen generating apparatus and nitrogen generating method - Google Patents

Nitrogen generating apparatus and nitrogen generating method Download PDF

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Publication number
CN116907177A
CN116907177A CN202310391115.7A CN202310391115A CN116907177A CN 116907177 A CN116907177 A CN 116907177A CN 202310391115 A CN202310391115 A CN 202310391115A CN 116907177 A CN116907177 A CN 116907177A
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CN
China
Prior art keywords
nitrogen
pressure
rotation speed
gas
compressor
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
CN202310391115.7A
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Chinese (zh)
Inventor
广濑献儿
永田大祐
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Original Assignee
LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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Filing date
Publication date
Application filed by LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude filed Critical LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Publication of CN116907177A publication Critical patent/CN116907177A/en
Pending legal-status Critical Current

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04006—Providing pressurised feed air or process streams within or from the air fractionation unit
    • F25J3/04012—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of warm gaseous streams; details of intake or interstage cooling
    • F25J3/0403—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of warm gaseous streams; details of intake or interstage cooling of nitrogen
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    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
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    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04006—Providing pressurised feed air or process streams within or from the air fractionation unit
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    • F25J3/04066—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of cold gaseous streams, e.g. intermediate or oxygen enriched (waste) streams of oxygen
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    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2250/00—Details related to the use of reboiler-condensers
    • F25J2250/20—Boiler-condenser with multiple exchanger cores in parallel or with multiple re-boiling or condensing streams
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2280/00—Control of the process or apparatus

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Health & Medical Sciences (AREA)
  • Emergency Medicine (AREA)
  • Separation By Low-Temperature Treatments (AREA)

Abstract

The present disclosure provides a nitrogen generating device capable of effectively controlling a compression expander in response to a variation in the supply pressure of product nitrogen gas. A nitrogen generating device (100) is provided with a main heat exchanger (1), a nitrogen rectifying tower (2), at least one nitrogen condenser, a compressor (6), an expansion turbine (7), a rotation control unit (8) for controlling the rotation of a rotation shaft connecting the compressor (6) and the expansion turbine (7), a pressure measuring unit (91) for measuring the pressure value of product nitrogen, and an optimal rotation speed calculation command unit (9), wherein the optimal rotation speed calculation command unit (9) inputs the pressure value measured by the pressure measuring unit (91) into a preset rotation speed calculation function, calculates the rotation speed of the rotation shaft, and gives a command to the rotation control unit (8).

Description

Nitrogen generating apparatus and nitrogen generating method
Technical Field
The present disclosure relates to a nitrogen generation apparatus and a nitrogen generation method for generating nitrogen from raw material air.
Background
The nitrogen generating device adopting the cryogenic air separation method is suitable for mass production of high-purity nitrogen. Such a nitrogen generator is suitable for supplying an inert gas and supplying a nitrogen raw material for ammonia synthesis or the like. The nitrogen generator includes a single rectification system (for example, patent document 1) having only 1 rectification column and a double rectification system (for example, patent document 2) having 2 or more rectification columns.
Regarding the product nitrogen gas supply pressure, the optimum pressure varies depending on the nitrogen gas utilization condition of the supply target (object). In the case of the double rectification system, since the product nitrogen gas is supplied from the low-pressure rectification column and the product nitrogen gas is compressed to the supply pressure by the product nitrogen compressor, the product nitrogen compressor discharge pressure can be controlled to optimize the product nitrogen gas according to the change in the required pressure. On the other hand, in the case of the single rectification method, by operating the rectification column at a pressure required for the supply of product nitrogen gas, nitrogen gas can be supplied without using a nitrogen compressor. However, if it is desired to follow the change in the required pressure of the supply target, the operating pressure of the rectifying column needs to be changed every time. When the operating pressure of the rectifying column is changed, the raw material air pressure is increased in accordance with the change, and for example, it is necessary to change the discharge pressure control value of the raw material air compressor.
Prior art literature
Patent document 1: U.S. patent No. 5,711,167
Patent document 2: U.S. patent No. 4,222,756
Disclosure of Invention
Problems to be solved by the invention
In the case of the nitrogen generating apparatus including the cold compression expander (cold booster expander) described in patent document 1, the operating pressure of the nitrogen condenser changes with a change in the operating pressure of the rectifying column, and thus the operating pressure condition of the compression expander changes. Further, the operating pressure of the rectifying column also affects the nitrogen separation efficiency and consequently also affects the nitrogen recovery rate, and therefore, in order to ensure the production amount of product nitrogen, the process flow rate of the compression expander must also be controlled. However, it is not practical to sequentially calculate and study the process pressure and flow balance from an arbitrary supply pressure and reset the control value, which is complicated and expensive. As a result, even when the product nitrogen gas can be supplied at a relatively low pressure, the product nitrogen gas supply pressure from the nitrogen generating device is set to the maximum value of the expected pressure demand, and eventually the difference between the demand pressure and the supply pressure becomes a loss of energy.
An object of the present disclosure is to provide a nitrogen generating apparatus and a nitrogen generating method capable of controlling a compressor (booster) and an expansion turbine (expander) more effectively than ever in response to a variation in the supply pressure of product nitrogen gas.
Means for solving the problems
The inventors of the present invention have found through intensive studies in simulation and actual equipment that the operating pressure of the rectifying column and the rotational speed of the compression/expansion machine are positively correlated with each other when the amount of nitrogen in the product is constant.
Table 1 shows that at a dose of 27300Nm 3 Raw air/h, 17000Nm produced 3 Optimal compressor operating conditions for each product nitrogen pressure in the case of product nitrogen per h.
TABLE 1
Product nitrogen pressure (barG) 8.8 9 9.2
Recycled air molar flow (Nm) 3 /h) 13822 14130 14438
Pressure of recirculated air (barA) when the compressor is suction 4.76 4.88 5.00
Recirculation air intake temperature (c) at compressor intake -170.9 -170.6 -170.3
Density of recirculated air (kg/m) at compressor suction 3 ) 22.9 23.4 23.8
Recycled air volume flow (m 3 /h) 792 794 796
As the product nitrogen pressure increases, the optimum recycle air molar flow increases. This is because, as the operating pressure of the rectifying column increases, the efficiency of rectification decreases, and thus the vapor stream needs to be increased in order to maintain the purity of the product nitrogen. The source of the recycle air is an oxygen-enriched liquid evaporated by heat exchange with nitrogen gas in the upper part of the rectifying column, and the temperature of the recycle air at the time of the suction of the compressor is lower than the temperature difference of the nitrogen condenser than the condensation point of the nitrogen gas, and the pressure of the recycle air is an equilibrium pressure at the temperature, so that the temperature and the pressure of the recycle air at the time of the suction of the compressor rise by the amount of the pressure rise of the product nitrogen gas. When the molar flow rate of the recirculation air and the temperature and pressure at the time of suction of the compressor were summarized and evaluated as the volume flow rate, it was found that the volume flow rate of the recirculation air increased in proportion to the increase in the nitrogen pressure. By using a function that uses the pressure of the rectifying column as a variable in this way, the optimal compression/expansion machine rotation speed can be estimated, and optimization of the process balance can be achieved without performing a complicated study.
This can be explained in principle as follows. When the pressure of the rectifying column increases, the recovery rate of the rectifying column decreases, and therefore, if the amount of product nitrogen is to be ensured, the amount of raw material air or the amount of recycled air needs to be increased, but since the increase of the amount of raw material air is against the reduction of energy consumption, it is desirable to increase the amount of recycled air. The amount of recirculated air in the compressor-expander is determined by the volumetric flow capacity of the impeller of the compressor and the accumulation of rotational speed of the rotating shaft of the compressor. The impeller structure is unchanged during the operation of the process conditions, and therefore the key is the rotational speed control.
Since the optimum amount of recycled air per process pressure is not obvious, studies have been carried out in the same apparatus comprising a rectifying column and a compression expander, over a range of pressures, with the result that a positive correlation (a correlation represented by a linear or nonlinear polynomial) is found between the rectifying column pressure and the volumetric flow rate of the recycled air, which can be easily reproduced by a polynomial. That is, it is clear that the volumetric flow rate of the recirculation air can be calculated as the accumulation of the volumetric flow rate processing capacity and the rotational speed of the impeller as described above, and therefore, the optimum recirculation air volumetric flow rate and the rotational speed setting value of the compression expander can be determined by a function of the rectifying column pressure as a variable, and the control point of the compression expander can be determined.
As a rotation speed calculation function for expressing a positive correlation (linear correlation), the following expression (1) is found.
y＝a×x+b (1)
Setting a rotating speed: y is
Coefficients: a, a
Product nitrogen pressure (pressure in piping upstream or downstream of the heat exchanger, pressure at any position of the nitrogen rectifying column): x is x
Correction value: b
As an arithmetic function for obtaining the raw material air pressure set value, the following expression (2) was found.
z＝d×x+e (2)
Raw material air pressure set point: z
Coefficients: d, d
Product nitrogen pressure: x is x
Correction value: e, e
Further, it was found that the rotation speed set point obtained by the rotation speed calculation function was adjusted by the following expression (3).
y’＝w×y (3)
The adjusted rotation speed set value: y'
Setting a rotating speed: y is
Coefficients: w (flow value of product nitrogen)
Each coefficient and correction value are set according to a simulation result corresponding to the device specification of the apparatus.
As the rotation speed calculation function, a nonlinear function may be used. Formula (11) is an example thereof.
y＝a 1 ×x+a 2 ×x 2 +a 3 ×x 3 +b 1 (11)
Setting a rotating speed: y is
Coefficients: a, a 1 、a 2 、a 3
Product nitrogen pressure (pressure in piping upstream or downstream of the heat exchanger, pressure at any position of the nitrogen rectifying column): x is x
Correction value: b 1
As an arithmetic function for obtaining the raw material air pressure set value, the following expression (12) is found.
z＝d×x+e (12)
Raw material air pressure set point: z
Coefficients: d, d
Product nitrogen pressure (pressure in piping upstream or downstream of the heat exchanger, pressure at any position of the nitrogen rectifying column): x is x
Correction value: e, e
Further, it was found that the rotation speed set point obtained by the rotation speed calculation function was adjusted by the following equation (13).
y’＝w×y (13)
The adjusted rotation speed set value: y'
Setting a rotating speed: y is
Coefficients: w (flow value of product nitrogen)
Each coefficient and correction value are set according to a simulation result corresponding to the device specification of the apparatus.
The nitrogen generating device of the present disclosure is configured such that raw material air is introduced from the lower part of a rectifying column, high-purity nitrogen gas is introduced from the upper part of the rectifying column, and the high-purity nitrogen gas can be taken out as product nitrogen gas.
The nitrogen generation device (100) of the present disclosure is provided with:
a main heat exchanger (1), into which main heat exchanger (1) raw air (feed air) is introduced;
a nitrogen rectifying column (2), wherein raw material air led out from the main heat exchanger (1) is introduced into a lower portion (22) of the nitrogen rectifying column (2);
at least one nitrogen condenser (first nitrogen condenser (3), second nitrogen condenser (4)) that condenses nitrogen gas that is led out from a column top (24) of the nitrogen rectifying column (2);
a compressor (6), wherein a first gas, which is led out from the top parts (32, 42) of the nitrogen condensers (3, 4), is led into the compressor (6);
a first gas recirculation pipe (L42) for introducing the first gas compressed by the compressor (6) into the lower part of the nitrogen rectifying column (2) through a part of the main heat exchanger (1);
an expansion turbine (7) through which the second gas, which is led out from the top (32, 42) of the nitrogen condenser (3, 4), passes through a part of the main heat exchanger (1) and is led into the expansion turbine (7);
a second gas outlet pipe (L32) for discharging the second gas used in the expansion turbine (7) through the main heat exchanger (1);
a rotation control unit (oil brake (8)) that controls rotation of a rotation shaft that connects the compressor (6) and the expansion turbine (7);
a product nitrogen gas take-out pipe (L24) for taking out the product nitrogen gas after passing the nitrogen gas, which is led out from the top (24) or upper rectifying part (23) of the nitrogen rectifying column (2), through the main heat exchanger (1);
a pressure measuring unit (91) that measures a pressure value at any part of the nitrogen rectifying column or a pressure value of the product nitrogen gas; and
and an optimal rotation speed calculation command unit (9) that calculates the rotation speed of the rotating shaft using the pressure value measured by the pressure measuring unit (91) in a preset rotation speed calculation function, and gives a command to the rotation control unit (8).
The pressure measuring unit (91) may be provided on the upstream side or downstream side of the main heat exchanger (1) of the product nitrogen gas extraction pipe (L24) to measure the pressure value of the product nitrogen gas.
The pressure measuring unit (91) can measure pressure values at any position of the top, the rectifying unit, and the bottom of the nitrogen rectifying tower.
The compressor (6) and the expansion turbine (7) may be configured by a compression expander provided with an oil brake, an expansion turbine-integrated compressor, or the like. The compressor-expander may be provided with a control nozzle or a bypass.
The optimal rotation speed calculation command unit (9) can control a flow control valve (94) provided in an oil introduction pipe for supplying oil to a rotation control unit (oil brake (8)), and can control the amount of oil supplied. A rotation angle measuring unit (93) for measuring the rotation angle of the motor of the flow control valve (94) can be provided. The optimal rotation speed calculation command unit (9) can read the rotation angle measured by the rotation angle measuring unit (94) and perform control (feedback control) so as to obtain the rotation speed obtained by the rotation speed calculation function.
The nitrogen generating device (100) may include a rotation measuring unit (92) for measuring the rotation speed of the rotation shaft,
the optimal rotation speed calculation command unit (9) and/or the rotation control unit (8) may control (feedback control) such that the rotation speed measured by the rotation measurement unit (92) becomes the rotation speed obtained by the rotation calculation function.
The nitrogen generation device (100) may be provided with:
a raw material air compressor (5) for controlling the supply pressure of raw material air upstream of the main heat exchanger (1); and
and a raw material air supply pressure control unit (95) that controls the discharge pressure set value of the raw material air compressor (5) based on the required pressure value of the product nitrogen gas or the pressure value measured by the pressure measurement unit (91).
The nitrogen generation device (100) may be provided with a liquid level measuring unit (211) for measuring the amount of the oxygen-enriched liquid at the bottom (21) of the nitrogen rectifying column (2),
the optimal rotation speed calculation command unit (9) and/or the rotation control unit (8) may limit the rotation speed so that the liquid amount measured by the liquid level measurement unit (211) falls within a preset setting range (upper limit and lower limit).
The nitrogen generating device (100) may be provided with a flow rate measuring unit (97) which is provided on the upstream side or downstream side of the main heat exchanger (1) of the product nitrogen gas extraction pipe (L24) and measures the flow rate value of the product nitrogen gas,
the optimal rotation speed calculation command unit (9) can adjust the rotation speed obtained by the rotation speed calculation function according to the flow rate measured by the flow rate measurement unit (97).
A pressure gauge, a thermometer, etc. may be provided in the nitrogen rectifying column (2) or other rectifying column (not shown).
Isolation valves, flow control valves, expansion valves, and the like may be provided in the product nitrogen gas take-out pipe (L24), the circulation pipe (L21), the first gas recirculation pipe (L42), the second gas discharge pipe (L32), and other various pipes.
A flowmeter, a manometer, a thermometer, etc. may be provided in the product nitrogen gas take-out pipe (L24), the circulation pipe (L21), the first gas recirculation pipe (L42), the second gas discharge pipe (L32), and other various pipes.
The nitrogen generation method of the present disclosure is a method for generating nitrogen by including at least a main heat exchanger, a nitrogen rectifying tower, at least one nitrogen condenser, a compressor, and an expansion turbine, and includes:
a rotation control step of controlling rotation of a rotation shaft connecting the compressor and the expansion turbine;
a pressure measurement step of measuring a pressure value of an arbitrary portion of the nitrogen rectifying column or a pressure value of product nitrogen; and
and an optimal rotation speed calculation command step of calculating the rotation speed of the rotating shaft connecting the compressor and the expansion turbine, using the pressure value measured in the pressure gauge measurement step, in a preset rotation speed calculation function, and commanding the rotation control step.
The feed air from the main heat exchanger may be directed into the lower portion of the nitrogen rectification column.
The nitrogen condenser may condense nitrogen gas led out from the top of the nitrogen rectification column.
A first gas, which is directed from the top of the column of the nitrogen condenser, may be directed to the compressor.
The second gas, which is led out from the top of the nitrogen condenser, may be led into the expansion turbine after passing through a part of the main heat exchanger.
The rotation control step may be performed by a rotation control unit that controls rotation of a rotation shaft that connects the compressor and the expansion turbine.
The pressure measuring step may be performed by a pressure measuring unit that measures a pressure value at any portion of the nitrogen rectifying column or a pressure value of the product nitrogen gas.
The optimal rotation speed calculation command step may be executed by calculating the rotation speed of the rotation shaft using a pressure value measured by the pressure measuring unit in a preset rotation speed calculation function, and by issuing a command to the rotation control unit.
Drawings
Fig. 1 is a configuration example of a nitrogen generating apparatus (air separation apparatus) according to embodiment 1.
Fig. 2 shows an example of the structure of a nitrogen generator (air separator) according to embodiment 2.
Fig. 3 is a configuration example of a nitrogen generating apparatus (air separation apparatus) according to embodiment 3.
Fig. 4 shows an example of the structure of a nitrogen generator (air separator) according to embodiment 4.
Description of the reference numerals
100. Nitrogen generating device (air separation plant)
1. Main heat exchanger
2. Nitrogen rectifying tower
3. First condenser
4. Second condenser
5. Raw material air compressor
6. Compressor with a compressor body having a rotor with a rotor shaft
7. Expansion turbine
8 rotation control part (oil brake)
9. Optimum rotation speed calculation instruction unit
91. Raw material air compressor
93. Air purifying device
95 raw material air supply pressure control unit
97. Flow meter measuring unit
211. Liquid level measuring part
L21 circulation piping
L24 product nitrogen gas takes out piping
L32 second gas outlet pipe
L42 first gas recirculation pipe
Detailed Description
Several embodiments of the present invention will be described below. The embodiment described below illustrates an example of the present invention. The present invention is not limited to the following embodiments, and includes various modifications that are implemented within a range that does not change the gist of the present invention. The structures described below are not necessarily all structures of the present invention.
(definition of terms)
In this specification, "upstream" and "downstream" are based on the flow of a gas (e.g., raw material air, first gas, second gas, nitrogen gas).
In the present specification, the "pressure value at any part of the nitrogen distillation column" refers to, for example, the pressure value at the top of the nitrogen distillation column or at the distillation part or bottom of the nitrogen distillation column.
(embodiment 1)
The nitrogen generating apparatus 100 according to embodiment 1 shown in fig. 1 is a unitary rectification type air separation apparatus.
The nitrogen generator 100 includes a main heat exchanger 1, a nitrogen rectifying column 2, a first nitrogen condenser 3, a second nitrogen condenser 4, a recycle gas compressor 6, and an expansion turbine 7 as basic structures.
The main heat exchanger 1 exchanges heat between raw material air (feed air) and other gases. The raw material air discharged from the main heat exchanger 1 is introduced into the lower portion 22 of the nitrogen rectifying column 2. The nitrogen rectifying column 2 has a bottom 21, a lower rectifying portion 22, an upper rectifying portion 23, and a top 24. The nitrogen gas discharged from the top 24 of the nitrogen rectifying column 2 is sent to the first nitrogen condenser 3 and the second nitrogen condenser 4, cooled by the cold and hot (cold) energy of the oxygen-enriched liquid, and returned to the nitrogen rectifying column 2. The oxygen-enriched liquid discharged from the bottom 21 of the nitrogen rectifying column 2 is introduced into the second condenser 4 through the circulation pipe L21 to be used as a cold and heat source, and is sent from the second condenser 4 to the first condenser 3 to be used as a cold and heat source.
In the present embodiment, the recirculated gas compressor 6 and the expansion turbine 7 are coupled to each other via a common rotation shaft, and are configured as a compression-expansion machine provided with an oil brake 8 for braking the rotation shaft. The oil brake 8 has a function of controlling the rotation of the rotary shaft (rotation control function).
The second gas led out from the top 32 of the first nitrogen condenser 3 passes through the second gas outlet pipe L32, passes through a part of the main heat exchanger 1, is sent to the expansion turbine 7, is used, passes through the main heat exchanger 1 again, and is discharged as exhaust gas (Wastegas).
The first gas (recycle gas) led out from the top 42 of the second nitrogen condenser 4 is sent to the recycle gas compressor 6 via the first gas recycle pipe L42, compressed, and sent to the lower rectifying portion 22 of the nitrogen rectifying column 2 through a part of the main heat exchanger 1.
The nitrogen gas discharged from the top 24 or the upper rectifying portion 23 of the nitrogen rectifying column 2 is sent to the main heat exchanger 1 through the product nitrogen gas discharge pipe L24 to exchange heat, and then supplied as product nitrogen gas to the supply point.
The pressure measuring unit 91 is provided downstream of the main heat exchanger 1 in the product nitrogen gas take-out pipe L24, and measures the pressure value of the product nitrogen gas. The optimal rotation speed calculation command unit 9 inputs the pressure value measured by the pressure measuring unit 91 into a preset rotation speed calculation function, calculates the rotation speed of the rotation shaft of the compressor/expander, and gives a command to the oil brake 8. In the present embodiment, the optimal rotation speed calculation command unit 9 controls the flow control valve 94 provided in the oil introduction pipe for supplying oil to the oil brake 8, and controls the supply amount of oil. The optimum rotation speed calculation command unit 9 is provided with a rotation angle measuring unit 93 for measuring the rotation angle of the motor of the flow control valve 94, and can read the rotation angle measured by the rotation angle measuring unit 93 and perform control (feedback control) so as to obtain the rotation speed obtained by the rotation speed calculation function.
As another embodiment, the pressure measuring unit 91 may be provided upstream of the main heat exchanger 1 of the product nitrogen gas extraction pipe L24, and may measure the pressure value of the product nitrogen gas, or may measure the pressure value at any position of the top and the rectifying unit of the nitrogen rectifying column 2.
The rotation speed calculation function is stored in a memory not shown.
In the present embodiment, the rotation speed calculation function is represented by the following expression (1).
y＝a×x+b (1)
Setting a rotating speed: y is
Coefficients: a, a
Product nitrogen pressure: x is x
Correction value: b
The coefficient a and the correction value b are set in advance according to the simulation result corresponding to the equipment specification and the implementation test of the device. The rotation speed calculation function is not limited to the expression (1), and may be a polynomial of a nonlinear function, and may be set according to the device specification.
(embodiment 2)
The nitrogen generating apparatus 100 according to embodiment 2 shown in fig. 2 further includes a raw material air compressor 5 in addition to the structure according to embodiment 1. The same reference numerals denote the same functions, and a structure having an additional function will be described in particular.
The raw material air compressor 5 controls the supply pressure of raw material air upstream of the main heat exchanger 1. The raw material air supply pressure control unit 95 controls the discharge pressure set value of the raw material air compressor 5 based on the required pressure value of the product nitrogen gas or the pressure value measured by the pressure measuring unit 91.
In the present embodiment, the raw material air supply pressure can be optimized according to the product nitrogen pressure, and the energy usage amount associated with the raw material air compression can be optimized. Specifically, for example, the power to be applied to the raw material air compressor 5 is adjusted by changing the discharge pressure set value of the raw material air compressor 5. An air cleaning device (93) may be provided between the raw air compressor 5 and the main heat exchanger 1.
The optimal rotation speed calculation command unit 9 or the raw material air supply pressure control unit 95 can calculate the discharge pressure set value. The discharge pressure set value can be obtained by the following expression (2).
z＝d×x+e (2)
Raw material air pressure set point: z
Coefficients: d, d
Product nitrogen pressure: x is x
Correction value: e, e
The coefficient d and the correction value e are set in advance according to the simulation result corresponding to the equipment specification and the implementation test of the device.
Embodiment 3
The nitrogen generating apparatus 100 according to embodiment 3 shown in fig. 3 further includes a liquid level measuring unit 211 in addition to the structure according to embodiment 2. The same reference numerals denote the same functions, and a structure having an additional function will be described in particular.
The liquid level measuring unit 211 measures the amount of the oxygen-enriched liquid located at the bottom 21 of the nitrogen rectifying column 2. The optimal rotation speed calculation command unit 9 limits the rotation speed so that the liquid amount measured by the liquid level measuring unit 211 falls within a preset setting range (upper limit value and lower limit value).
Thus, the rotational speed control of the compression/expansion machines (6, 7) can be adjusted according to the liquid level at the bottom 21 of the nitrogen rectifying column 2. By the brake system, the heat content is discharged from the process gas to the outside by using a medium such as heat or electric power, and thus the process gas is cooled accordingly. This is referred to as supplying cold (cold energy) to the process gas. In a deep-cooling type air separation apparatus such as the nitrogen generator 100, it is important to obtain liquefied air as a reflux liquid, and therefore, it is necessary to sufficiently supply cold. In general, in order to maintain the operation of the nitrogen generating device, it is desirable to maintain some liquefied air in the device, and thus, for example, some liquid level in the space of the bottom 21 of the nitrogen rectification column 2. On the other hand, in the present embodiment, when the rotational speed control of the compression/expansion machine is changed according to the pressure change of the product nitrogen gas, there is a concern that the supply of cold to the process is insufficient (for example, when the rotational speed is increased). Therefore, as in the present embodiment, the operation control liquid level is set in advance, and the variation range of the control rotation speed is limited so as not to deviate from the control range. Thus, even if the required pressure changes more greatly, the device can be kept continuously operating without shortage of cold.
Embodiment 4
The nitrogen generating apparatus 100 according to embodiment 4 shown in fig. 4 further includes a flow rate measuring unit 97 in addition to the structure according to embodiment 3. The same reference numerals denote the same functions, and a structure having an additional function will be described in particular.
The flow rate measuring unit 97 is provided downstream of the main heat exchanger 1 in the product nitrogen gas take-out pipe L24, and measures the flow rate value of the product nitrogen gas. The optimal rotation speed calculation command unit 9 adjusts the rotation speed obtained by the rotation speed calculation function based on the flow rate measured by the flow rate measuring unit 97.
According to the present embodiment, the rotation speed can be adjusted (proportionally) to the flow rate of the product nitrogen gas with respect to the rotation speed obtained from the pressure of the product nitrogen gas.
The rotation speed set value obtained by the rotation speed calculation function is adjusted by the following expression (3).
y’＝w×y (3)
The adjusted rotation speed set value: y'
Setting a rotating speed: y (obtained from the above formula (1))
Coefficients: w (adjustment coefficient according to the flow value of product nitrogen)
The coefficient w is preset according to the simulation result corresponding to the equipment specification and the implementation experiment of the device.
The optimal rotation speed calculation command unit 9 and the raw material air supply pressure control unit 95 may be realized by cooperation of a computer having a processor and a memory and a software program stored in the memory, or may be realized by a dedicated circuit, firmware, or the like, and may include an input/output interface and an output unit.
(nitrogen production method)
As for the nitrogen generation method, the nitrogen generation apparatus described above may be used to generate nitrogen, or may be executed in another device.
The nitrogen generation method of the present disclosure is a method for generating nitrogen by including at least a main heat exchanger, a nitrogen rectifying tower, at least one nitrogen condenser, a compressor, and an expansion turbine, and includes:
a rotation control step of controlling rotation of a rotation shaft connecting the compressor and the expansion turbine;
a pressure measurement step of measuring a pressure value of an arbitrary portion of the nitrogen rectifying column or a pressure value of product nitrogen; and
and an optimal rotation speed calculation command step of calculating the rotation speed of the rotating shaft connecting the compressor and the expansion turbine, using the pressure value measured in the pressure gauge measurement step, in a preset rotation speed calculation function, and commanding the rotation control step.
The feed air from the main heat exchanger may be directed into the lower portion of the nitrogen rectification column.
The nitrogen condenser may condense nitrogen gas led out from the top of the nitrogen rectification column.
A first gas, which is directed from the top of the column of the nitrogen condenser, may be directed to the compressor.
The second gas, which is led out from the top of the nitrogen condenser, may be led into the expansion turbine after passing through a part of the main heat exchanger.
The rotation control step may be performed by a rotation control unit that controls rotation of a rotation shaft that connects the compressor and the expansion turbine.
The pressure measuring step may be performed by a pressure measuring unit that measures a pressure value at any portion of the nitrogen rectifying column or a pressure value of the product nitrogen gas.
The optimal rotation speed calculation command step may be executed by calculating the rotation speed of the rotation shaft using a pressure value measured by the pressure measuring unit in a preset rotation speed calculation function, and by issuing a command to the rotation control unit.
The product nitrogen gas take-out pipe may be a pipe through which the nitrogen gas discharged from the top or upper rectifying portion of the nitrogen rectifying column passes through the main heat exchanger and then the product nitrogen gas is taken out.
The first gas recirculation pipe may introduce the first gas compressed by the compressor to a lower portion of the nitrogen rectifying column through a part of the main heat exchanger.
The second gas outlet pipe may be a pipe for discharging the second gas used in the expansion turbine through the main heat exchanger.
The nitrogen generation method may be controlled (feedback control) in the optimum rotation speed calculation instruction step and/or the rotation control step so that the rotation speed measured by the rotation measuring unit that measures the rotation speed of the rotation shaft becomes the rotation speed obtained by the rotation speed calculation function.
The nitrogen generation method may include a raw material air supply pressure control step of controlling a discharge pressure set value of a raw material air compressor for controlling a supply pressure of raw material air upstream of the main heat exchanger based on a required pressure value of the product nitrogen gas or a pressure value measured in the pressure measurement step.
In the nitrogen generation method, the rotation speed may be limited in the optimum rotation speed calculation instruction step and/or the rotation control step so that the liquid amount measured by a liquid level measuring unit that measures the amount of the oxygen-enriched liquid located at the bottom of the nitrogen rectifying column falls within a preset set range (upper limit and lower limit).
In the above-described nitrogen generation method, in the optimum rotation speed calculation command step, the rotation speed obtained by the rotation speed calculation function may be adjusted based on the flow rate measured by the flow rate measuring unit that measures the flow rate value of the product nitrogen gas on the upstream side or the downstream side of the main heat exchanger.
(other embodiments)
(1) The nitrogen generator may include a first rectifying column (high-pressure rectifying column) for rectifying the liquefied air, a first nitrogen condenser, and a second rectifying column (low-pressure rectifying column) for leading out and further rectifying the crude oxygen from which the high-boiling components (e.g., methane and the like) are removed from the high-pressure rectifying column. The high pressure rectifying column may be a nitrogen making rectifying column. Nitrogen can be withdrawn from the nitrogen-making rectification column. The low pressure rectification column may be an oxygen production rectification column.
(2) In embodiments 1 to 4, the rotation speed is adjusted by the oil brake, but the rotation speed is not limited thereto, and the rotation speed may be substantially controlled by driving a generator connected to the expansion turbine and recovering the generator as electric energy.

Claims (5)

1. A nitrogen generating device is provided with:
a main heat exchanger into which raw air is introduced;
a nitrogen rectifying column into the lower part of which raw material air led out from the main heat exchanger is introduced;
at least one nitrogen condenser condensing nitrogen gas led out from a top of the nitrogen rectifying column;
a compressor to which a first gas introduced from a top of the nitrogen condenser is introduced;
a first gas recirculation pipe for introducing the first gas compressed by the compressor to a lower portion of the nitrogen rectifying column through a part of the main heat exchanger;
an expansion turbine to which the second gas introduced from the top of the nitrogen condenser is introduced after passing through a part of the main heat exchanger;
a second gas outlet pipe for discharging the second gas used in the expansion turbine through the main heat exchanger;
a rotation control unit that controls rotation of a rotation shaft that connects the compressor and the expansion turbine;
a product nitrogen gas take-out pipe for taking out the product nitrogen gas after passing the nitrogen gas discharged from the top or upper rectifying portion of the nitrogen rectifying column through the main heat exchanger;
a pressure measuring unit that measures a pressure value of an arbitrary portion of the nitrogen rectifying column or a pressure value of the product nitrogen gas; and
and an optimal rotation speed calculation command unit that calculates the rotation speed of the rotating shaft using the pressure value measured by the pressure measuring unit in a preset rotation speed calculation function, and gives a command to the rotation control unit.
2. The nitrogen generating apparatus according to claim 1, comprising:
a raw material air compressor for controlling a supply pressure of raw material air upstream of the main heat exchanger; and
and a raw material air supply pressure control unit that controls a discharge pressure set value of the raw material air compressor based on the required pressure value of the product nitrogen gas or the pressure value measured by the pressure measurement unit.
3. The nitrogen generating device according to claim 1 or 2, comprising:
a liquid level measuring unit for measuring the amount of the oxygen-enriched liquid at the bottom of the nitrogen rectifying column,
the optimal rotation speed calculation command unit and/or the rotation control unit limits the rotation speed so that the liquid amount measured by the liquid level measuring unit falls within a preset setting range.
4. The nitrogen generation apparatus according to any one of claims 1 to 3, comprising:
a flow rate measuring unit provided on the upstream side or downstream side of the main heat exchanger of the product nitrogen gas extraction pipe and configured to measure a flow rate value of the product nitrogen gas,
the optimal rotation speed calculation command unit adjusts the rotation speed obtained by the rotation speed calculation function based on the flow rate measured by the flow rate measurement unit.
5. A nitrogen generation method is provided with at least a main heat exchanger, a nitrogen rectifying tower, at least one nitrogen condenser, a compressor and an expansion turbine, and includes:
a rotation control step of controlling rotation of a rotation shaft connecting the compressor and the expansion turbine;
a pressure measurement step of measuring a pressure value of an arbitrary portion of the nitrogen rectifying column or a pressure value of product nitrogen; and
and an optimal rotation speed calculation command step of calculating the rotation speed of the rotating shaft connecting the compressor and the expansion turbine, using the pressure value measured in the pressure gauge measurement step, in a preset rotation speed calculation function, and commanding the rotation control step.
CN202310391115.7A 2022-04-15 2023-04-13 Nitrogen generating apparatus and nitrogen generating method Pending CN116907177A (en)

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